Method and system for replacing a pattern in a layout

ABSTRACT

A received layout identifies a plurality of circuit components to be included in an integrated circuit (IC) layer for double patterning the layer using two photomasks, the layout including a plurality of first patterns to be included in the first photomask and at least one second pattern to be included in the second photomask. A selected one of the first patterns has first and second endpoints, to be replaced by a replacement pattern connecting the first endpoint to a third endpoint. At least one respective keep-out region is provided adjacent to each respective remaining first pattern except for the selected first pattern. Data are generated representing the replacement pattern, such that no part of the replacement pattern is formed in any of the keep-out regions. Data representing the remaining first patterns and the replacement pattern are output.

FIELD

The present disclosure relates to semiconductor fabrication generallyand more specifically to multi-patterning, such as double patterning.

BACKGROUND

In semiconductor fabrication processes, the resolution of a photoresistpattern begins to blur at about 45 nanometer (nm) half pitch. Tocontinue to use fabrication equipment purchased for larger technologynodes, double exposure methods have been developed.

Double exposure involves forming patterns on a single layer of asubstrate using two different masks in succession. As a result, aminimum line spacing in the combined pattern can be reduced whilemaintaining good resolution. In a method referred to as double dipolelithography (DDL), the patterns to be formed on the layer are decomposedand formed on a first mask having only horizontal lines, and on a secondmask having only vertical lines. The first and second masks are said tohave 1-dimensional (1-D) patterns, which can be printed with existinglithographic tools.

Another form of double exposure is referred to as double patterningtechnology (DPT). Unlike the 1-D approach of DDL, DPT in some casesallows a vertex (angle) to be formed of a vertical segment and ahorizontal segment on the same mask. Thus, DPT generally allows forgreater reduction in overall IC layout than DDL does. DPT is a layoutsplitting method analogous to a two coloring problem for layoutsplitting in graph theory. The layout polygon and critical space aresimilar to the vertex and edge of the graph respectively. Two adjacentvertices connected with an edge should be assigned different colors. Ifonly two masks are to be used, then only two “color types” are assigned.Each pattern on the layer is assigned a first or second “color”; thepatterns of the first color are formed by a first mask, and the patternsof the second color are formed by a second mask. A graph is 2-colorableonly if it contains no odd loop.

In terms of graph theory, when the total number of relationships betweenpatterns that violate the minimum threshold spacing for a single mask(referred to as the separator distance) is odd, an odd loop is present,and DPT cannot be used without changing the layout.

In some cases, after a layout has proceeded through double patterningdecomposition, and photomasks are produced, the designer discovers anunderlying logic error in the design, which must be corrected through adesign change (e.g., an engineering change order). Such a design changemay require new photomasks, at added expense. Because two masks are usedfor a single layer, the added expense is doubled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a first embodiment of the method.

FIG. 2 is a diagram of a pre-colored layout having a selected pattern tobe replaced.

FIG. 3 shows the layout of FIG. 2, with the selected pattern removed.

FIG. 4 shows the layout of FIG. 3, with keep-out regions added.

FIG. 5 shows the layout of FIG. 4 with the replacement pattern added.

FIG. 6 shows the final layout, with the replacement pattern added.

FIG. 7 is a flow chart of a first embodiment of the method.

FIG. 8 is a diagram of a partially-colored layout having a selectedpattern to be replaced.

FIG. 9 shows the layout of FIG. 8, with the selected pattern removed.

FIG. 10 shows the layout of FIG. 9, with keep-out regions added.

FIG. 11 shows the layout of FIG. 10 with the replacement pattern added.

FIG. 12 shows the final layout, with the replacement pattern added.

FIG. 13 is a block diagram of the system.

DETAILED DESCRIPTION

This description of the exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the description, relativeterms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,”“below,” “up,” “down,” “top” and “bottom” as well as derivative thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should beconstrued to refer to the orientation as then described or as shown inthe drawing under discussion. These relative terms are for convenienceof description and do not require that the apparatus be constructed oroperated in a particular orientation. Terms concerning attachments,coupling and the like, such as “connected” and “interconnected,” referto a relationship wherein structures are secured or attached to oneanother either directly or indirectly through intervening structures, aswell as both movable or rigid attachments or relationships, unlessexpressly described otherwise.

This description of the exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the description, relativeterms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,”“below,” “up,” “down,” “top” and “bottom” as well as derivative thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should beconstrued to refer to the orientation as then described or as shown inthe drawing under discussion. These relative terms are for convenienceof description and do not require that the apparatus be constructed oroperated in a particular orientation. Terms concerning attachments,coupling and the like, such as “connected” and “interconnected,” referto a relationship wherein structures are secured or attached to oneanother either directly or indirectly through intervening structures, aswell as both movable or rigid attachments or relationships, unlessexpressly described otherwise.

To minimize the added expense of implementing a design change afterdouble-patterning decomposition (especially after photomaskfabrication), it is desirable to minimize the number of masks that arechanged to implement the design change. If the double patterningdecomposition tool is given complete freedom to implement the modifieddesign, the tool may make changes to both (or all) photomasks for themodified layer, increasing expense.

In some embodiments, one available technique is to keep all of thepatterns fixed, except for the selected pattern that is to be removed,and construct “keep-out” regions adjacent to (or surrounding) all theother patterns. The replacement pattern is not permitted to intersectany of the keep-out regions. By only routing the replacement patternoutside of the keep-out regions, the system can ensure that the minimumseparator distance between two patterns formed by the same photomask ismaintained. The replacement pattern routing is constrained so as not tointersect any of the other patterns, or any of the keep-out regions.This technique limits the change to a single mask—the mask containingthe replacement pattern. However, if every pattern is surrounded by akeep-out region, the layout may become so filled with keep-out regionsthat it becomes impossible to reroute the selected pattern whileavoiding all of the keep-out regions.

The inventors have determined that improved re-routing is achieved if nokeep-out regions are constructed adjacent to patterns that are known tobe formed on a different photomask from the selected pattern that is tobe replaced. This method may be used in two different situations.

In the first situation, referred to herein as “pre-coloring”, the user(e.g., designer or foundry engineer) knows on which photomask eachpattern in the layer is formed, including the selected pattern to bereplaced and its replacement pattern. In other words, the user knows thecolor of every pattern. In this case, keep-out regions are onlyconstructed adjacent to patterns that are known to be formed on the samephotomask as the selected pattern that is to be replaced. Thereplacement pattern is rerouted so as to not intersect any of thekeep-out regions or the patterns on the other mask.

In the second situation, referred to herein as “partial-coloring”, theuser does not know on which photomask each pattern in the layer isformed. For example, the user may be a design house engineer, and thefoundry may only give the user partial information in order to keepcertain processes and software as trade secret information. The user isonly given a subset of the patterns that are formed on the samephotomask as the selected pattern, and a subset of the patterns that areformed on a different photomask from the selected pattern. The user isgiven no color information with respect to the remaining patterns, whichmay be on either mask. Although the user has no color information aboutthe remaining patterns, the remaining patterns have been assigned toparticular masks. These assignments, even though unknown to the user,constrain the routing of the replacement pattern. In this case,“keep-out” regions are only constructed adjacent to patterns that areknown to be formed on the same photomask as the selected pattern that isto be replaced, and adjacent to patterns for which the mask assignmentis unknown. The replacement pattern is rerouted so as to not intersectany of the keep-out regions or the patterns known to be assigned to adifferent mask than the selected pattern.

FIG. 1 is a flow chart of the first embodiment. FIGS. 2-6 show anexample of the application of a method to a layer of an integratedcircuit.

At step 100 of FIG. 1, a layout is received identifying a plurality ofcircuit components to be included in an integrated circuit (IC) layerfor double patterning the layer using first and second photomasks. Forexample, the layer 200 (FIG. 2) may be a copper metal layer of theinterconnect structure of an IC, to be formed by a dual damasceneprocess. The layout 200 includes a plurality of first patterns 220, 230,231 to be included in the first photomask and at least one secondpattern 240, 241, 242, 243 to be included in the second photomask. Inthe example, a cell 210, is also provided from an IP library ofpre-existing cell designs. The layout data may be received from amachine readable storage medium of a computer system of a foundry or adesigner. The data are received by an automated system (described belowwith reference to FIG. 13) for rerouting one of the patterns.

At step 102 of FIG. 1, the system receives an identification of aselected one of the first patterns 220 having a first endpoint 221 and asecond endpoint 222. The selected pattern 220 is to be replaced by areplacement pattern 260 (FIG. 6) connecting the first endpoint 221 to athird endpoint 223. For example, the user may have determined that adesign change is appropriate to change the circuit connected to the cell210. The user may identify the selected pattern 220 by using a pointingdevice coupled to a computer that graphically displays all the patternsof the layer. In other embodiments, the user may select a text entryfrom a netlist defining the layout.

At step 104 of FIG. 1, the system removes the selected pattern 220 fromthe layout 200. FIG. 3 is a schematic view of the layout 200 at thisstage. The IP cell 210 now has an unconnected pin 221. In someembodiments, the system displays this intermediate stage to the userduring the process.

At step 106 of FIG. 1, the system reserves at least one respectivekeep-out region 250 (FIG. 4). adjacent to each respective remainingfirst pattern 230 except for the selected first pattern 220 (which hasalready been removed). In some embodiments, each respective keep-outregion 250 surrounds its corresponding first pattern 230 on all sidesthereof. For example, in some embodiments, the keep-out regiondimensions are determined by multiplying each dimension of the patternto be surrounded by a constant. In another embodiment, the pattern 230is decomposed into individual rectangles, and a keep-out region 250a-250 c is constructed around each of the individual components of thepattern 230. By constructing individual keep-out region portions 250a-250 c for each component of a complex pattern 230, the overall size ofthe keep-out region 250 is minimized. This type of keep-out region canbe implemented through the technology file of the electronic designautomation (EDA) tool, to selectively increase the size of theindividual rectangles making up pattern 230.

In some embodiments, pattern 231 is a rectangle, and a respectivekeep-out region 251 around that rectangle has a perimeter, such that theperimeter has a first distance d1 from a longer side of the rectangle251, and the perimeter has a second distance d2 from a shorter side ofthe rectangle. Other techniques may be used to construct the keep-outregion.

In the example of FIG. 4, patterns 240, 241, 242 and 243 are known to beassigned to the second mask, which is different from the first maskhaving the selected pattern 220. Thus, no keep-out regions areconstructed adjacent to patterns 240-243.

At step 108 of FIG. 1, the system generates data representing thereplacement pattern 260 (FIG. 5), such that no part of the replacementpattern 260 is formed in any of the keep-out regions 250. Becausepatterns 240-243 are formed on another mask, there is no need tomaintain the minimum separation distance between the replacement patternand patterns 240-243 (so long as the replacement pattern does notintersect second patterns 240-243). Thus, the distance 270 between thereplacement pattern 260 on the first photomask and pattern 242 on thesecond mask can be less than the minimum separator distance for twolines on the same photomask.

At step 110 of FIG. 1, the system outputs data representing theremaining first patterns 230, 231 and the replacement pattern 260 to amachine readable storage medium to be read to fabricate the firstphotomask. The data representing the remaining first patterns and thereplacement pattern form a double patterning compliant set of photomasklayouts without rerouting any of the at least one second patterns. Insome embodiments, the data are output in a GDS II format, compatiblewith the output of the EDA tool. In other embodiments, the data areoutput in a proprietary format. Optionally, the system may provide agraphical output of the layout to the user, as shown in FIG. 6.

At step 112, the rerouting is implemented by a change to the first maskonly, without affecting the second mask. In the example shown in FIG. 6,the patterns 241 and 242 are so close together, that the router might beunable to generate a pattern connecting the endpoints 221 and 223 ifkeep-out regions were reserved around the patterns 241 and 242. Byomitting the keep-out regions around patterns that are known to beassigned to the second photomask, the system provides enough flexibilityfor the router to quickly find the pattern 260.

At step 114, the first mask is fabricated. If the second mask haspreviously been fabricated, there is no need to replace the secondphotomask.

Although the first example describes an embodiment with only twophotomasks, the method can be extended to ICs in which three or moremasks are used to pattern one layer. In step 106, the system onlyreserves keep-out regions for the same mask in which the selectedpattern is formed. No keep-out regions are reserved in any of the othermasks. At step 108, the replacement pattern is rerouted to avoidintersecting any of the keep-out regions and to avoid intersecting anyof the patterns on any of the photomasks.

FIG. 7 is a flow chart of a variation of the method, in which the userhas only partial knowledge regarding the assignment of the patterns tothe two photomasks (partial coloring).

At step 700 of FIG. 7, the system receives an integrated circuit (IC)layout 300 (FIG. 8) for double patterning a layer of the IC using firstand second photomasks. The layout 300 includes a plurality of circuitpatterns, at least one of which is an uncolored pattern. For example,the user may be a designer, who informs a foundry that he needs toreroute the pattern 320, and the user's system receives a partiallycolored layout. In FIG. 8, the user's system receives informationindicating that pattern 324 is on the same mask as pattern 320, andpatterns 340, 341 and 342 are on a different mask. The user's system isaware that patterns 350 and 351 are to be fabricated on the same metallayer of the IC, but has no knowledge as to whether or not patterns 350and 351 are formed by the same mask as patterns 320 and 324.

At step 702 of FIG. 7, the user's system receives an identification of aselected one of the plurality of circuit patterns 320 having firstendpoint 321 and a second endpoint 322, to be replaced by a replacementpattern connecting the first endpoint 321 to a third endpoint 323,without receiving an indication in steps 700 or 702 of whether theuncolored patterns 350, 351 are to be included in the first photomask orthe second photomask. For example, the user may input the identificationby selecting the pattern 320 using a graphical user interface, or theuser may input the information by text information, using a netlistformat.

At step 704 of FIG. 7, the system removes the selected pattern 320 fromthe layout. The result is shown in FIG. 9.

At step 706 of FIG. 7, the system reserves at least one keep-out region361, 362 adjacent to the at least one uncolored pattern 350, 351,respectively. Because the color information for these patterns is notavailable, they are treated as though they are on the same photomask asthe selected pattern 320. The system also reserves at least one keep-outregion 360 adjacent to the region(s) 324 identified as being in the samemask as the selected pattern 320. No keep-out regions are reserved forthe regions 340, 341 and 342, which are identified as being on adifferent photomask from the selected pattern. The resulting layout isshown in FIG. 10.

In some multi-patterning embodiments, where more than two photomasks areused, all patterns identified as being on a different photomask from theselected pattern 320 are treated identically to each other. No keep-outregions are reserved for any pattern assigned to any of the photomasksother than the photomask on which the selected pattern 320 is provided.

At step 708 of FIG. 7, the system generates data representing thereplacement pattern 370, such that no part of the replacement pattern370 intersects any of the plurality of circuit patterns 340-342 or anyof the keep-out regions 360, 361, 362. The result is shown in FIG. 11.Because no keep-out region is reserved for the patterns 340-342, therouter can route the replacement pattern 370, so that a distance betweenpattern 370 and one or more of the patterns 340-342 is closer than theminimum separator distance for patterns to be formed on the samephotomask as each other.

At step 710 of FIG. 7, the system outputs data representing thereplacement pattern, to be combined with data representing ones of theplurality of circuit patterns to be formed on the same photomask as thereplacement pattern, on a machine readable storage medium to be read tofabricate the same photomask.

At step 712 of FIG. 7, the rerouting has been implemented to replace theselected pattern 320 with the replacement pattern 370 in the samephotomask, so as to form a complete set of layouts for double patterningthe layer with a change to only the same photomask, without changing alayout of the other of the first and second photomasks. The result isshown in FIG. 12. Note that the user is unaware that patterns 350 and351 are actually formed on the same mask as the replacement pattern 370.By reserving the keep-out regions adjacent the uncolored patterns, thesystem ensures that the layer can be patterned regardless of whether theuncolored patterns 350 and 351 are formed on the same photomask as thereplacement pattern.

Although the second example describes an embodiment with only twophotomasks, the method can be extended to ICs in which three or moremasks are used to pattern one layer. In step 706, the system reserveskeep-out regions around patterns in the same mask in which the selectedpattern is formed and around all uncolored patterns. No keep-out regionsare reserved for any patterns identified as being in a different maskfrom the selected pattern. At step 708, the replacement pattern isrerouted to avoid intersecting any of the keep-out regions and to avoidintersecting any of the patterns on any of the photomasks.

At step 714 of FIG. 7, the system forms the first photomask containingthe replacement pattern 370 and the patterns 324, 350 and 351. Thus there-routing has been accomplished with a change to only one mask.

FIG. 13 is a block diagram of a system 400 for rerouting a selectedpattern 220, according to one embodiment. Block 402 indicates that oneor more programmed processors may be included. In some embodiments, theprocessing load is performed by two or more application programs, eachoperating on a separate processor. In other embodiments, the processesare all performed using one processor. Similarly, two media 406 and 408are shown, but the data may be stored in any number of media. AlthoughFIG. 13 shows an allocation of the various tasks to specific modules,this is only one example. The various tasks may be assigned to differentmodules to improve performance, or improve the ease of programming.

System 400 includes an electronic design automation (“EDA”) tool 402such as “IC COMPILER”™, sold by Synopsys, Inc. of Mountain View, Calif.,which may include a place and route tool 404, such as “ZROUTE”™, alsosold by Synopsys. Other EDA tools 402 may be used, such as the“VIRTUOSO” custom design platform or the Cadence “ENCOUNTER” digital ICdesign platform may be used, along with the “VIRTUOSO” chip assemblyrouter 404, all sold by Cadence Design Systems, Inc. of San Jose, Calif.

EDA tool 402 is a special purpose computer formed by retrieving storedprogram instructions from a non-transient computer readable storagemedium 406, 408 and executing the instructions on a general purposeprocessor (not shown). Examples of non-transient computer readablestorage mediums 406, 408 include, but are not limited to, read onlymemories (“ROMs”), random access memories (“RAMs”), flash memories, harddisk drives, optical disk, or the like. Tangible, non-transient machinereadable storage mediums 406, 408 are configured to store data generatedby the place and route tool 404.

Place and route tool 404 is capable of receiving an identification of aplurality of cells to be included in an integrated circuit (“IC”) orinterposer layout,. The place and route tool 404 places the cells fromthe IP library and lays out the connecting patterns to connect theinput/output pins of the cells. The place and route tool 404 may beequipped with a set of default design rules 422 and technology file 424.

The “collect pre-coloring information” module 410 provides the usertools for selecting one or more patterns to be replaced. In someembodiments, module 410 display the layout of a metal layer with theavailable color information, as shown in FIG. 2 or FIG. 8. The modulereceives the user's selection of the pattern(s) to be replaced, andrequests/retrieves the available coloring information, which may becomplete pre-coloring information (assignments of all patterns) orpartial coloring information (subset of patters on same mask as selectedpattern, a subset of patterns on different masks, and the remaininguncolored patterns).

The keep-out region generation module 412 constructs the appropriatekeep-out regions for all patterns (if any) known to be on the samephotomask as the selected pattern, and for all patterns (if any) forwhich color information is not available to the system.

The replacement pattern generation module 414 determines the replacementpattern 260, so as to avoid intersection with any of the keep-outregions and avoid intersection with any of the patterns.

In some embodiments, a routing method comprises: (a) receiving a layoutidentifying a plurality of circuit components to be included in anintegrated circuit (IC) layer for double patterning the layer usingfirst and second photomasks, the layout including a plurality of firstpatterns to be included in the first photomask and at least one secondpattern to be included in the second photomask; (b) receiving anidentification of a selected one of the first patterns having first andsecond endpoints, to be replaced by a replacement pattern connecting thefirst endpoint to a third endpoint; (c) reserving at least onerespective keep-out region adjacent to each respective remaining firstpattern except for the selected first pattern; (d) generating datarepresenting the replacement pattern, such that no part of thereplacement pattern is formed in any of the keep-out regions; and (e)outputting data representing the remaining first patterns and thereplacement pattern to a machine readable storage medium to be read tofabricate the first photomask.

In some embodiments, a routing method comprises: (a) receiving anintegrated circuit (IC) layout for double patterning a layer of the ICusing first and second photomasks, the layout including a plurality ofcircuit patterns, at least one of which is an uncolored pattern; (b)receiving an identification of a selected one of the plurality ofcircuit patterns having first and second endpoints, to be replaced by areplacement pattern connecting the first endpoint to a third endpoint,without receiving an indication in step (a) or (b) of whether theuncolored pattern is to be included in the first photomask or the secondphotomask; (c) removing the selected pattern from the layout; (d)reserving at least one keep-out region adjacent to the at least oneuncolored pattern; (e) generating data representing the replacementpattern, such that no part of the replacement pattern intersects any ofthe plurality of circuit patterns or the at least one keep-out region;and (f) outputting data representing the replacement pattern, to becombined with data representing ones of the plurality of circuitpatterns to be formed on the same photomask as the replacement pattern,on a machine readable storage medium to be read to fabricate the samephotomask.

In some embodiments, a persistent machine readable storage medium isencoded with computer program code, such that when the computer programcode is executed by a processor, the processor performs a methodcomprising: (a) receiving an identification of a plurality of circuitcomponents to be included in an integrated circuit (IC) layout fordouble patterning a layer using first and second photomasks, theidentification including a plurality of first patterns to be included inthe first photomask and at least one second pattern to be included inthe second photomask; (b) receiving an identification of a selected oneof the first patterns having first and second endpoints, to be replacedby a replacement pattern connecting the first endpoint to a thirdendpoint; (c) reserving at least one respective keep-out region adjacentto each respective remaining first pattern except for the selected firstpattern; (d) generating data representing the replacement pattern, suchthat no part of the replacement pattern is formed in any of the keep-outregions; and (e) outputting data representing the remaining firstpatterns and the replacement pattern to a machine readable storagemedium to be read to fabricate the first photomask.

In some embodiments, a persistent machine readable storage medium isencoded with computer program code, such that when the computer programcode is executed by a processor, the processor performs a methodcomprising: (a) receiving an integrated circuit (IC) layout for doublepatterning a layer of the IC using first and second photomasks, thelayout including a plurality of circuit patterns, at least one of whichis an uncolored pattern; (b) receiving an identification of a selectedone of the plurality of circuit patterns having first and secondendpoints, to be replaced by a replacement pattern connecting the firstendpoint to a third endpoint, without receiving an indication in step(a) or (b) of whether the uncolored pattern is to be included in thefirst photomask or the second photomask; (c) removing the selectedpattern from the layout; (d) reserving at least one keep-out regionadjacent to the at least one uncolored pattern; (e) generating datarepresenting the replacement pattern, such that no part of thereplacement pattern intersects any of the plurality of circuit patternsor the at least one keep-out region; and (f) outputting datarepresenting the replacement pattern, to be combined with datarepresenting ones of the plurality of circuit patterns to be formed onthe same photomask as the replacement pattern, on a machine readablestorage medium to be read to fabricate the same photomask.

In some embodiments, a system comprises: a programmed processor coupledto at least one persistent, machine readable storage medium. The mediumhas a first storage portion storing data representing a layoutidentifying a plurality of circuit components to be included in anintegrated circuit (IC) layer for double patterning the layer usingfirst and second photomasks, the layout including a plurality of firstpatterns to be included in the first photomask and at least one secondpattern to be included in the second photomask. The at least one mediumhas a second storage portion for storing an identification of a selectedone of the first patterns having first and second endpoints, to bereplaced by a replacement pattern connecting the first endpoint to athird endpoint. The processor is configured for: (a) reserving at leastone respective keep-out region adjacent to each respective remainingfirst pattern except for the selected first pattern; (b) generating datarepresenting the replacement pattern, such that no part of thereplacement pattern is formed in any of the keep-out regions; and (c)outputting data representing the remaining first patterns and thereplacement pattern to a machine readable storage medium to be read tofabricate the first photomask.

In some embodiments, a system comprises: a programmed processor coupledto at least one persistent, machine readable storage medium. The mediumhas a first storage portion storing data representing an integratedcircuit (IC) layout for double patterning a layer of the IC using firstand second photomasks, the layout including a plurality of circuitpatterns, at least one of which is an uncolored pattern. The at leastone medium has a second storage portion for receiving an identificationof a selected one of the plurality of circuit patterns having first andsecond endpoints, to be replaced by a replacement pattern connecting thefirst endpoint to a third endpoint, without receiving an indication ofwhether the uncolored pattern is to be included in the first photomaskor the second photomask. The processor is configured for: (a) removingthe selected pattern from the layout; (b) reserving at least onekeep-out region adjacent to the at least one uncolored pattern; (c)generating data representing the replacement pattern, such that no partof the replacement pattern intersects any of the plurality of circuitpatterns or the at least one keep-out region; and (d) outputting datarepresenting the replacement pattern, to be combined with datarepresenting ones of the plurality of circuit patterns to be formed onthe same photomask as the replacement pattern, on a machine readablestorage medium to be read to fabricate the same photomask.

The methods and system described herein may be at least partiallyembodied in the form of computer-implemented processes and apparatus forpracticing those processes. The disclosed methods may also be at leastpartially embodied in the form of tangible, non-transient machinereadable storage media encoded with computer program code. The media mayinclude, for example, RAMs, ROMs, CD-ROMs, DVD-ROMs, BD-ROMs, hard diskdrives, flash memories, or any other non-transient machine-readablestorage medium, wherein, when the computer program code is loaded intoand executed by a computer, the computer becomes an apparatus forpracticing the method. The methods may also be at least partiallyembodied in the form of a computer into which computer program code isloaded and/or executed, such that the computer becomes a special purposeapparatus for practicing the methods. When implemented on ageneral-purpose processor, the computer program code segments configurethe processor to create specific logic circuits. The methods mayalternatively be at least partially embodied in a digital signalprocessor formed of application specific integrated circuits forperforming the methods.

Although the subject matter has been described in terms of exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be construed broadly, to include other variants and embodiments,which may be made by those skilled in the art.

What is claimed is:
 1. A routing method comprising: (a) receiving alayout identifying a plurality of circuit components to be included inan integrated circuit (IC) layer for double patterning the layer usingfirst and second photomasks, the layout including a plurality of firstpatterns to be included in the first photomask and at least one secondpattern to be included in the second photomask; (b) receiving anidentification of a selected one of the first patterns having first andsecond endpoints, to be replaced by a replacement pattern connecting thefirst endpoint to a third endpoint; (c) reserving at least onerespective keep-out region adjacent to each respective remaining firstpattern except for the selected first pattern; (d) generating datarepresenting the replacement pattern, such that no part of thereplacement pattern is formed in any of the keep-out regions; (e)outputting data representing the remaining first patterns and thereplacement pattern to a machine readable storage medium to be read tofabricate the first photomask.
 2. The method of claim 1, wherein step(c) includes: for each remaining first pattern, generating a respectivekeep-out region surrounding that remaining first pattern on all sidesthereof.
 3. The method of claim 2, wherein one of the first patterns isa rectangle, and a respective keep-out region around that rectangle hasa perimeter, such that: the perimeter has a first distance from a longerside of the rectangle, and the perimeter has a second distance from ashorter side of the rectangle.
 4. The method of claim 1, wherein thereplacement pattern and the second pattern do not intersect, and aminimum distance between the replacement pattern and the second patternis less than a minimum separation distance between two patterns to beformed on the same photomask.
 5. The method of claim 1, wherein: thedata representing the replacement pattern is generated so that thereplacement pattern does not intersect any of the at least one keep-outregion or the second pattern, and steps (c) and (d) are performedwithout generating a keep-out region abutting the second pattern.
 6. Themethod of claim 1, wherein the data representing the remaining firstpatterns and the replacement pattern output in step (e) and the at leastone second pattern to be included in the second photomask identified instep (a) form a double patterning compliant set of photomask layoutswithout rerouting any of the at least one second patterns.
 7. The methodof claim 1, further comprising forming the first and second photomasksafter step (e).
 8. A routing method comprising: (a) receiving anintegrated circuit (IC) layout for double patterning a layer of the ICusing first and second photomasks, the layout including a plurality ofcircuit patterns, at least one of which is an uncolored pattern; (b)receiving an identification of a selected one of the plurality ofcircuit patterns having first and second endpoints, to be replaced by areplacement pattern connecting the first endpoint to a third endpoint,without receiving an indication in step (a) or (b) of whether theuncolored pattern is to be included in the first photomask or the secondphotomask; (c) removing the selected pattern from the layout; (d)reserving at least one keep-out region adjacent to the at least oneuncolored pattern; (e) generating data representing the replacementpattern, such that no part of the replacement pattern intersects any ofthe plurality of circuit patterns or the at least one keep-out region;(f) outputting data representing the replacement pattern, to be combinedwith data representing ones of the plurality of circuit patterns to beformed on the same photomask as the replacement pattern, on a machinereadable storage medium to be read to fabricate the same photomask. 9.The method of claim 8, wherein: steps (e) and (f) implement replacementof the selected pattern by the replacement pattern in the samephotomask, so as to form a complete set of layouts for double patterningthe layer with a change to only the same photomask, without changing alayout of the other of the first and second photomasks.
 10. The methodof claim 8, wherein: the layout received in step (a) identifies aplurality of first patterns to be formed in the same one of thephotomasks as the selected pattern and a plurality of second patterns tobe formed in a different one of the photomasks from the selectedpattern, the method further comprising: reserving at least oneadditional keep-out region adjacent to each of the first patternswithout reserving a keep-out region adjacent to any of the secondpatterns, and step (e) includes generating data representing thereplacement pattern, such that no part of the replacement patternintersects any of the additional keep-out regions.
 11. The method ofclaim 10, wherein: the layout received in step (a) identifies aplurality of uncolored patterns; the method further comprises reservingat least one further keep-out region adjacent to each respective one ofthe uncolored patterns; and no part of the replacement patternintersects any of the further keep-out regions.
 12. The method of claim8, wherein: the layout received in step (a) identifies a plurality ofuncolored patterns; the method further comprises reserving at least onefurther keep-out region adjacent to each respective one of the uncoloredpatterns; and no part of the replacement pattern intersects any of thefurther keep-out regions.
 13. The method of claim 8, wherein thekeep-out region surrounds the uncolored pattern on all sides thereof.14. The method of claim 8, further comprising forming the first andsecond photomasks after step (f).
 15. A persistent machine readablestorage medium encoded with computer program code, such that when thecomputer program code is executed by a processor, the processor performsa method comprising: (a) receiving an identification of a plurality ofcircuit components to be included in an integrated circuit (IC) layoutfor double patterning a layer using first and second photomasks, theidentification including a plurality of first patterns to be included inthe first photomask and at least one second pattern to be included inthe second photomask; (b) receiving an identification of a selected oneof the first patterns having first and second endpoints, to be replacedby a replacement pattern connecting the first endpoint to a thirdendpoint; (c) reserving at least one respective keep-out region adjacentto each respective remaining first pattern except for the selected firstpattern; (d) generating data representing the replacement pattern, suchthat no part of the replacement pattern is formed in any of the keep-outregions; (e) outputting data representing the remaining first patternsand the replacement pattern to a machine readable storage medium to beread to fabricate the first photomask.
 16. The machine readable storagemedium of claim 15, wherein step (c) includes: for each remaining firstpattern, generating a respective keep-out region surrounding thatremaining first pattern on all sides thereof.
 17. The machine readablestorage medium of claim 16, wherein one of the first patterns is arectangle, and a respective keep-out region around that rectangle has aperimeter, such that: the perimeter has a first distance from a longerside of the rectangle, and the perimeter has a second distance from ashorter side of the rectangle.
 18. The machine readable storage mediumof claim 15, wherein the replacement pattern and the second pattern donot intersect, and a minimum distance between the replacement patternand the second pattern is less than a minimum separation distancebetween two patterns to be formed on the same photomask.
 19. The machinereadable storage medium of claim 15, wherein: the data representing thereplacement pattern is generated so that the replacement pattern doesnot intersect any of the at least one keep-out region or the secondpattern, and steps (c) and (d) are performed without generating akeep-out region abutting the second pattern.
 20. The machine readablestorage medium of claim 15, wherein the data representing the remainingfirst patterns and the replacement pattern output in step (e) and the atleast one second pattern to be included in the second photomaskidentified in step (a) form a double patterning compliant set ofphotomask layouts without rerouting any of the at least one secondpatterns.